This invention relates to high pressure sealing joints or connections and more particularly to an annular bore seal for sealing between first and second coaxially aligned tubular members having different coefficients of thermal expansion or which are joined together by metal fastening means having a different coefficient of thermal expansion. The present invention has, as its primary object, the provision of a high pressure bore seal with a unique metallic sealing ring which maintains elasticity at its sealing surface areas and the ability to maintain a fluid-tight seal under high pressure and high temperature conditions even though the joined members or the fastening means for the joined members may have a different coefficient of thermal expansion.
During a fire, several conditions occur which cause conventional seals and gaskets to fail. First and most obvious, many conventional seals utilize non-metallic materials on the sealing surfaces and these materials break down or degrade at high temperatures such as to cause the seal to leak. Also, the high alloy bolting materials needs for high temperature and fire resistant applications, are almost always of different material than the joined tubular members. Accordingly, with heat, the bolts expand a greater amount than the low and intermediate alloy steels of which the flanges are made. This differential thermal expansion results in a reduction of the bolting preload. Most conventional seals and gaskets depend on bolt loading to produce the contact pressure necessary to effect a seal and if the contact pressure is reduced by thermal expansion to less than the contained fluid pressure, the seal will leak. If flange separation occurs, conventional gaskets will fail castastrophically.
Another condition which adversely effects conventional seal designs during a fire is the distortion of the seal grooves with heat. This problem is further complicated by the fact that the seal grooves of the mating flanges do not distort in the same way or in the same amount in a fire due to uneven heat distribution and differences between the cross sections of the mating flanges. A conventional gasket design sandwiches a sealing material between two flanges. Uneven radial deformation will damage the sealing surface and result in a leak.
Other seal designs, such as shown in U.S. Pat. No. 4,408,771 depend on mismatched angles between the sealing ring and the cooperating sealing surface to produce the necessary contact pressure for sealing. As the seal grooves deform during a fire, these seals are pushed outward by pressure to follow the outward movement of the groove. The accompanying loss of desirable physical properties of the sealing ring such as tensile strength and yield strength of the seal may result in bending of the seal ring and loss of the mismatch. Also, if the grooves of the joined members deform by different amounts, angular mismatch will be altered or eliminated with the least bit of outward radial deformation. A reduction in angular mismatch increases the contact area, decreasing the contact pressure. If the contact pressure at any point is less than the contained pressure, the seal will leak.